1. Field of the Invention
The present invention relates to an apparatus and a method for detecting channel information; and, more particularly, the present invention relates to an apparatus and a method for monitoring channel status and detecting location and a number of working channels from a wavelength division multiplexed (WDM) signal without demultiplexing the WDM signals by using a wavelength selective detector (herein, in the WDM signal, a wavelength means a channel).
2. Description of the Prior Art
A status of an individual channel is an important factor in terms of management, maintenance and monitoring performance of network. Switching and recovering operations should be rapidly performed in accordance with a channel status when there is an error in optical network, since a lot of information are transmitted through transmission channel at a high speed (e.g., 10 Gbps or more than 10 Gbps). Thus, the status information for each channel should be monitored rapidly, correctly, simply, and in an economical way.
In a wavelength division multiplexed optical transmission system and an optical transport network, presence of individual channel cannot be identified without demultiplexing the wavelength division multiplexed signal, since lots of channels, each channel having a different wavelength, are transmitted as mixed.
FIG. 1 is a diagram illustrating a WDM channel detector in accordance with a conventional method. The WDM channel detector comprises an optical multiplexer 11, an optical amplifier 12, an optical coupler 13, an optical demultiplexer 14, a photo detector 15 and a signal processor 16.
Optical signals, each of which has a different wavelength, are multiplexed by the optical multiplexer 11. The multiplexed optical signals are divided into individual channel at the optical demultiplexer 14. Thereafter, it is determined that the channel is presented or not on the basis of the divided signals. Thus, there existed disadvantages that lots of optical elements, such as the optical demultiplexer 14 and the photo detectors 15 (D1 to Dn), are needed, thereby additional loss of optical power resulted from use of the demultiplexer 14 is caused. Such a conventional WDM. channel detector is described in U.S. Pat. No. 5,617,234 issued to M. Koga, entitled of xe2x80x9cMultiwavelength simultaneous monitoring circuit employing arrayed-waveguide gratingxe2x80x9d.
FIG. 2 is a diagram illustrating another conventional WDM channel detector. The WDM detector comprises an optical multiplexer 21, an optical amplifier 22, an optical coupler 23, a variable optical filter 24, a waveform counter 25 and an optical detector 27.
The waveform counter 25 detects presence and location of working channels from wavelength division multiplexed optical signals scanned through a tunable optical filter 24 and optical-to-electrical converted through a photo detector 27. An article by C. Konishi, xe2x80x9cDynamic gain controlled erbium doped fiber amplifier repeater for WDM networkxe2x80x9d, OFC""97 Paper TuE1, pp18-19, 1997, shows an example of method for checking the presence of channel by using the tunable optical filter 24 without demultiplexing the WDM signals such as shown in FIG. 2. Even though the optical demultiplexer 14 is not used in Konishi""s method contrary to the above mentioned U.S. Pat. No. 5,617,234, there are demerits that the tunable optical filter 24 such as an expensive Acousto Optic Tunable Filter(AOTF) is necessarily needed, and that a detection speed is restricted due to scanning of the tunable optical filter 24. Moreover, there is a disadvantage in Konishi""s method that processing of signal in a tunable optical filter controller 26 and a waveform counter 25 is relatively complicated.
Therefore, it is an object of the present invention to provide an apparatus and a method for detecting channel information from wavelength division multiplexed signals without demultiplexing the wavelength division multiplexed signals.
It is another object of the present invention to provide an apparatus and a method for detecting channel information from wavelength division multiplexed signals without using complicated and expensive devices.
It is still another object of the present invention to provide an apparatus and a method for more rapidly detecting channel information from wavelength division multiplexed signals without delay due to scanning.
In accordance with one embodiment of the present invention, there is provided an apparatus for detecting channel information in each channel from wavelength division multiplexed (WDM) optical signals each having a different wavelength, comprising: a pre-processor for pre-processing WDM optical signals and outputting a portion of the WDM optical signals; a photo detector for converting the WDM optical signal from said pre-processor into a first electrical signal having a constant value regardless of wavelengths of the WDM optical signal; a wavelength selective photo detector for converting the WDM optical signal from said pre-processor into a second electrical signal having a different value in response to the wavelength of the distributed optical signal; a lookup table for storing the wavelengths, a number of channels and optical power per channel; normalization part for normalizing the second electrical signal with respect to the first electrical signal; channel number detector for detecting a number of channels using the optical power per channel and power of the first electrical signal; and channel location detector for detecting channel locations by using normalized electrical signals and electrical power values stored in said lookup table.
In accordance with another embodiment of the present invention, there is provided a method for detecting channel information from wavelength division multiplexed optical signals each having a different wavelength, comprising the steps of: a) storing wavelengths to be used as channls, a number of channel, an optical power per a channel and electrical power values, each of the electrical power value corresponding to a channel combination specifying location of working channel in a lookup table; b) pre-processing WDM optical signals and outputting a portion of the WDM optical signals; c) converting pre-processed WDM optical signal into a first electrical signal having a constant value regardless of wavelengths of the WDM optical signal; d) converting the pre-processed WDM optical signal into a second electrical signal having a different value in response to the wavelength of the WDM optical signal; e) normalizing the second electrical signal with respect to the first electrical signal; f) detecting a number of channels using the optical power per channel and power of the first electrical signal; and g) detecting channel location by using normalized electrical signals and electrical power values stored in the lookup table.
In accordance with still another embodiment of the present invention, there is provided a computer-readable recording medium, tangibly embodying a program of instruction executable by the machine to perform a method for detecting channel information from wavelength division multiplexed signals each having a different wavelength, said programs of the instruction running in a data processing machine, the method comprising the steps of: a) storing wavelengths to be used as channels, a number of channel, electrical power values for one channel (almost all the same) and each electrical power corresponding to a channel combination specifying location of working channel in a lookup table; b) pre-processing WDM optical signals and outputting a portion of the WDM optical signals; c) converting the WDM optical signal pre-processed into a first electrical signal having a constant value regardless of wavelengths of the WDM optical signal; d) converting the WDM optical signal pre-processed into a second electrical signal having a different value in response to the wavelength of the WDM optical signal; e) normalizing the second electrical signal with respect to the first electrical signal; f) detecting a number of channels using the electrical power corresponding to one channel and power of the first electrical signal; and g) detecting channel location by using normalized electrical signals and electrical power values stored in the lookup table.